The field of the present invention is pug mills for mixing and conditioning clay for ceramics.
Pug mills are designed for producing clay conditioned for the manufacture of ceramics. The mills typically are used to mix clay powder and water or rehydrate, remix and/or recondition existing clay. Powders and water may also be mixed with existing clay to form a homogeneous product. The clay, once mixed, is most conveniently extruded through a reduction cone to form cylindrical or rectangular blocks also known as pugs.
Pug mills upon which the present design is based are disclosed in U.S. Pat. No. 4,322,169 entitled CLAY MIXING APPARATUS and U.S. Pat. No. 5,716,130 entitled VACUUM PUG MILL, the disclosures of which are incorporated herein by reference in their entirety. These pug mills include a mixing chamber expending to an extruder in communication therewith. A shaft is rotatably mounted relative to the mixing chamber and the extruder. Mixing blades associated with the mixing chamber are fixed to the shaft as is an auger associated with the extruder. The shaft is rotatably mounted by bearings such that an extension of the shaft through the mixing chamber and the extruder is cantilevered from the bearings. The bearings are positioned in a housing including a drive motor and drive train for forcibly rotating the shaft. The shaft is rotatable in either direction about its axis. When rotated in a first direction, mixing takes place. When rotated in a second direction, the clay is advanced by the mixing blades and by the auger for extrusion through the reduction cone.
In addition to the conditioning of clay to achieve an appropriate moisture content and homogeneity, it is advantageous to remove as much air as possible. Air entrapped in the clay when fired can expand to ruin the article manufactured. Also, entrapped air can adversely affect throwing operations as it makes the clay “short” and hard to work with. The pug mill disclosed in U.S. Pat. No. 5,716,130 provides a vacuum chamber in communication with the mixing chamber for drawing a vacuum on the clay to remove air from being mixed into the clay. A cover on the end of the reduction cone or a solid body of clay being extruded therefrom provides a sealed mixing chamber to permit the drawing of the vacuum.
U.S. Pat. No. 5,716,130 provides a mechanism for maintaining a clear communication port between the mixing chamber and the vacuum chamber of that mill. It remains that material being pugged can still overwhelm the communication port and interrupt the application of vacuum in the mixing chamber.